Measurement of electrolytes (e.g., sodium, potassium, calcium, and magnesium) and analytes (e.g., glucose) and assessment of blood levels of medications can be important in clinical medicine. This importance spans a large panoply of disease states including arrhythmias, heart failure, renal failure, and medication titration or adjustment. Assessment of these values involves access to blood—either by phlebotomy or other skin puncture.